The current invention relates to regulation of the temperature in the brain and spinal cord. The invention describes a method and apparatus for altering the temperature of the brain surface and/or the cerebrospinal fluid in the ventricles of the brain and surrounding the spinal cord.
Hypothermia has been shown to provide cerebral and spinal cord injury protection from either trauma, ischemia, or hypoxia. Ischemia may occur from cardiac arrest, cardiac failure, stroke, head or spinal cord injury, aneurysm surgery, cardiac surgery, and aortic or carotid surgery. Hypothermia is also effective in reducing increased intracranial pressure from cerebral swelling. The mechanisms involved in hypothermic cerebral protection are several-fold and include 1) reduction in cerebral glucose and oxygen metabolism and decreasing lactate content following injury, 2) preventing disruption of the blood brain barrier and consequently reducing cerebral edema, 3) reduction of endogenously toxic neurotransmitters like glutamate, glycine, aspartate, acetylcholine, and norepinephrine into the brain after injury, 4) inhibit excessive calcium entry and intracellular calcium overload into neurons, 5) protecting membrane structural proteins like microtubule-associated protein-2, and 6) preventing diffuse axonal injury following brain trauma.
In general, the human brain and spinal cord are maintained at a constant temperature of approximately 37 to 38 degrees celsius. Hypothermia is considered mild when the body temperature is 33 to 35 degrees celsius, moderate between the temperatures of 28 to 32 degrees, and severe in the temperature range of 24 to 28 degrees celsius. Most studies in humans have involved mild to moderate systemic hypothermia mainly because of the significant side effects that occur from induced systemic hypothermia. These include infection, cardiac arrhythmias, coagulopathy, renal failure, as well as rewarming shock. In order to avoid these complications the degree and duration of hypothermia has been shortened thereby limiting its effectiveness.
Generally, cooling of the brain has been accomplished through whole body cooling with use of a cooling blanket, immersing the patient in ice, or cooling the blood through a cardiopulmonary bypass machine. A few methods have been described regarding selective brain and spinal cord hypothermia. These involve cooling the arterial vessel or blood supply to the brain or external cooling helmets, each with its own significant limitations.
Several catheters have been developed to induce systemic hypothermia by inserting them into the bloodstream. More recently catheters have been developed that can be inserted into the arterial vessels to the brain to induce selective brain hypothermia. These catheters are limited in their size and finctionality by the small vessel lumen as well the inability to cool all the four major arterial vessels supplying blood to the brain and are unable to cool the spinal cord via this methodology. They also carry the risk of ischemic and thromboembolic stroke by either impairing the blood flow to the brain or dislodging clots that can develop in intra-arterial catheters.
External cooling helmets have limited effectiveness since the blood to the cooled scalp does not circulate into the brain and returns systemically which along with the thick skull dilutes the hypothermic effect to the brain.
Selective brain and spinal cord cooling with insertion of catheters into the ventricular, subdural or epidural space as described in U.S. Pat. No. 6,699,269 to Khanna is a novel concept. It also describes a catheter that expands with circulation of a coolant without direct contact of the coolant with the central nervous system. This avoids the side effects and complications seen from other methods of cooling. It also circumvents infection and fluid overload with exacerbation of brain swelling that can be potentially encountered with cooling systems involving circulating the cerebrospinal fluid. Implanted catheters are prone to the complications of obstruction and infection. In order to circumvent these complications, strategies have been developed which include use of systemic or local antibiotics and impregnating catheter walls with antibiotics and metals. While these methodologies have shown some effectiveness, the risk of complications still remains high. Several catheters capable of delivering ultrasonic or laser energy for blood clot hemolysis have been described. There is no prior art for a catheter with the capability of selective brain hypothermia induction and ultrasound or laser energy use to maintain catheter patency. The use of ultrasound and/or laser energy along with anti-clotting and antimicrobial agents is also a novel concept and prevents catheter obstruction from blood clots and debris as well as infection.